bbs的树形结构显示可以有很多种方法，其中比较容易想到的是递归和排序串方法，但这两种方法并不是很好，那么怎样才算是比较合理的算法呢？
    递归方法不用讲，大家都知道怎么用，先讲讲排序串方法，最简单的排序串方法可以这样用,只用一个id就可以完成树型，向这样
1  001
2  002
3  001001
4  001001001
5  001002001
用这个字符串排序后就变成这样：
001
   001001
         001001001
   001002001
002
这种方法容易实现，但缺点也是很明显，一个是回帖数受限制，另一个随着回帖增加会越来越长，影响数据库效率。  

下面一种方法是李龙的，属于变通的排序串方法
DDL
--------------
CREATE TABLE dbo.Message
(
    ID          numeric(18,0) IDENTITY(1000,1),
    DateAndTime datetime      DEFAULT getdate() NOT NULL,
    AuthorID    numeric(18,0) NOT NULL,
    Subject     nvarchar(250) NOT NULL,
    Body        ntext         NULL,
    LinkURL     nvarchar(100) NULL,
    TextForLink nvarchar(50)  NULL,
    ImageURL    nvarchar(100) NULL,
    Class       int           DEFAULT 0 NOT NULL,
    ClientInfo  nvarchar(250) NULL,
    RemoteAddr  nvarchar(50)  NULL,
    CONSTRAINT PK_BBSMessage
    PRIMARY KEY NONCLUSTERED (ID,AuthorID)
)
go
CREATE TABLE dbo.MsgRefTab
(
    MsgID      numeric(18,0) NOT NULL,
    ParentID   numeric(18,0) NOT NULL,
    AncestorID numeric(18,0) NOT NULL,
    ChildNum   numeric(18,0) DEFAULT 0 NOT NULL,
    LinkStr    nvarchar(250) NOT NULL,
    CONSTRAINT PK_BBSRefTab
    PRIMARY KEY NONCLUSTERED (MsgID)
)
go
-----------------
存储过程:
-----------------
-- 抽出
CREATE PROCEDURE sp_Summary
HaveBody bit,
from numeric,
to numeric
AS
IF (HaveBody = 1)
select t.ID,t.DateAndTime,m.Nickname as
Author,m.Email,t.Subject,t.Body,t.LinkURL,t.TextForLink,t.ImageURL,s.ChildNu
m,s.ParentID
from Message t
  ,MsgRefTab AS s
  ,(SELECT MsgID FROM MsgRefTab WHERE ParentID = 0) AS f
  ,Members AS m
where t.ID=s.MsgID
  and f.MsgID = s.AncestorID
  and f.MsgID between from and to
  and m.MemberID = t.AuthorID
order by s.AncestorID,s.LinkStr
ELSE
select t.ID,t.DateAndTime,m.Nickname as
Author,m.Email,t.Subject,t.LinkURL,t.TextForLink,t.ImageURL,s.ChildNum,s.Par
entID
from Message t
  ,MsgRefTab AS s
  ,(SELECT MsgID FROM MsgRefTab WHERE ParentID = 0) AS f
  ,Members AS m
where t.ID=s.MsgID
  and f.MsgID = s.AncestorID
  and f.MsgID between from and to
  and m.MemberID = t.AuthorID
order by s.AncestorID,s.LinkStr
go

-- 加贴

CREATE PROCEDURE sp_Add_Message
AuthorID numeric,
Subject nvarchar(250),
Body  ntext,
LinkURL nvarchar(100),
TextForLink nvarchar(50),
ImageURL nvarchar(100),
ParentID numeric,
ID  numeric OUTPUT,
ChildNum numeric OUTPUT,
LinkStr nvarchar(250) OUTPUT,
AncestorID numeric OUTPUT
AS
INSERT INTO Message(
  AuthorID,
  Subject,
  Body,
  LinkURL,
  TextForLink,
  ImageURL)
VALUES(
  AuthorID,
  Subject,
  Body,
  LinkURL,
  TextForLink,
  ImageURL)

SELECT ID = IDENTITY

UPDATE MsgRefTab
SET
  ChildNum = ChildNum+1
WHERE
  MsgID = ParentID

SELECT ChildNum = ChildNum,
  LinkStr = LinkStr,
  AncestorID =